After an extensive investigation lasting well over a year, NPR's ombudsman has concluded the network's series on South Dakota's efforts to put Native American children in foster care was fundamentally flawed.

The network and the ombudsman, Edward Schumacher-Matos, who is paid to critique NPR's news coverage, have split sharply over his findings.

The series, which appeared in October 2011 on All Things Considered and was published on NPR.org, alleged that the state of South Dakota took Native American children and separated them from their families and tribes at an alarming rate. The series won national awards and helped inspire federal and state reviews of such policies.

NPR correspondent Laura Sullivan reported over many months with producer Amy Walters, who now works for Al Jazeera America. The stories present a wrenching tale in South Dakota. American Indians make up 15 percent of the state's population, but, as Sullivan told listeners in October 2011, they account for more than half the children in foster care.

"It's not hard to find them," she reported. "There are thousands of them: Native Americans with missing children."